Hello,
I have a few questions about some tests, but i won't be able to attend the reharsal meeting due to a test the day after. this is why i am asking here and not there.

ds06aa question 3:
"T(n)=T(upper(n/2))+T(lower(n/2))+teta(n). which algorithms' worst case does it represent?"
the official answer is MERGESORT+QUICKSORT. I don't understand why this is true for QUICKSORT. if the input's size is 10, then the subproblems are at size 4 and 5, none of which is upper(n/2). and if the size of the input is 9, then the subproblems are at size 4,4, again non of which is upper(n/2). so why is it true?